1. Field
Example embodiments relate to an apparatus and method for detecting data stored in a memory cell, and more particularly, to apparatuses and methods for hybrid detection that performs hard decision detection and soft decision detection.
2. Description of Related Art
A single-level cell (SLC) memory device may store one data bit in a single memory cell. The SLC memory may be referred to as a single-bit cell (SBC) memory. The SLC memory may store and read one data bit at a voltage level included in two distributions that are divided by a threshold voltage level programmed in a memory cell. The programmed threshold voltage has a distribution within a certain range due to a fine electric characteristic difference between the SLC memories. For example, when a voltage level read from the memory cell is greater than 0.5V and less than 1.5V, it may be determined that the data stored in the memory cell has a logic value of “1”. When the voltage level read from the memory cell is greater than 2.5V and less than 3.5V, it may be determined that the data stored in the memory cell has a logic value of “0”. The data stored in the memory cell may be classified depending on the difference between cell currents and/or cell voltages during the reading operations.
Meanwhile, a multi-level cell (MLC) memory device that may store data of two or more bits in a single memory cell has been proposed in response to a need for higher integration of memory. The MLC memory device may also be referred to as a multi-bit cell (MBC) memory. However, as the number of bits stored in the single memory cell increases, reliability deteriorates and read-failure rate may increase. To store “m” bits in a single memory cell, 2N voltage level distributions may be required. However, since the voltage window for a memory device is limited, the difference in threshold voltage between adjacent bits may decrease as “N” increases, causing the read-failure rate to increase. For this reason, it may be difficult to improve storage density using the MLC memory device according to conventional art.